Isomerization of aromatic compounds



Patented Dec. 30, 1952 NITED' STATES ISQMERIZATION F- AEGMATIG COMPOUNDS Ben Bennett Corson and Joseph E. Nickels, Pittsburgh, Pa., assignors to Koppers- Company, Inc.,

12 Claims.

This invention relates to isomerization of aromatic compounds. More particularly the invention relates to. the. alkylation. and the isomerization of alkylated aromatic hydrocarbons and phenols wherein the alkylated aromatic compounds are capable of existing in two or more isomeric forms. lhe aromatic compounds to which the invention specifically relates are the alkyl naphthalenes, the dialkylbenzenes, and the alkylphenols.

When aromatic compounds, such as naphthalene, benzene and phenols are alkylated, generally more than one isomeric form of alkylated product is formed, depending upon the raw' materials alkylated and the process of alkylation used. It is usually quite difficult to separate these isomers because of their closely related boiling points and, therefore, an isomerization treatment of the products will often assist in obtaining a separation.

In the application of Walter M. Kutz, Serial No. 760-626 filed July 12, 1947, now U. S. Patent 2,515,237 issued July18, 1950, is described a procsee by. which naphthalene may be alkylated with ethylene in the liquid phase at a temperature of 300 C. when passing the reaction products through. a solid. bed of, catalyst composed of alumina activated, with silica. This catalyst is preferably a synthetic product made up of" 99% S102 and1% A1203. This catalyst is very reactive so that it, is desirable. tohold the temperature low to. avoid lossby formation of fixed gases and carbon and the formation of polyethylnaphthalene.

The alumina activated silica will give a product made up of approximately 80% bet-aethylnaphthalene and 20% of alpha-ethylnaphthalene. The reaction would appear to be a combined alkylation and isomerization reaction because catalysts suchas iron phosphate and 'hydrogen fluoride, which act only as alkylation catalysts for alkylating naphthalene with ethylene, give a product made up of from 47% to 56 alphaethylnaphthalene and 53% to 44% betaethylnaphthalene. On the other hand, if a 5lle50 mixture of alpha-- and 'betaethy-lnaphthalenes is isomerized with the aluminaactivated silica catalyst a product is obtained which is composed of approximately betaethylnaphthalene and 20 alphaethylnaphthalene.

We have found that a mixture of 78% to 32% betaethylnaphthalene. withv 22% tov 18% alphaethylnaphthalene is an equilibrium mixture which may be obtained either by the so-called combined catalytic alkylation and isomerization reaction of naphthalene with ethylene, or by a catalytic isomerization of a mixture of betaethylnaphthalene and alphaethylnaphthalene with an alumina activated silica catalyst.

Experience has shown that the loss of raw'materials involved in the use of an alumina activated silica catalyst will vary from 5 to 15% of' the starting material under favorable operating conditions. We have found that the equilibrium mixture of approximately 80 b etaethylnaphthalene and 20% alphaethylnaphthalene can be obtained by the alkylation of naphthalenewith ethylene, or from the isomerizationof almostany. mixture. of alphaand betaethylnaphthalenes by reaction in the presence of steam with a silica. catalyst. containing from 3 to 10 of; analkali metal carbonate or oxide, or amixture of the. alkali metal carbonate and oxide. The. presence of an-alkaline compound of an alkali metal in the catalyst tends to decrease the activity of the silica alumina catalyst, but this catalyst with themodified activity will yield an equilibrium mixtureof betaand alphaethylnaphthalenes-with 2. 00111- paratively low loss of raw'materials. Furtherthe presence of the alkaliv metal compoundinthecatalyst will act to convert anycarbon formed in the reaction to carbon oxide gases so: that the carbon is not deposited on, the catalyst to; lower its activity. V

The primary object of the present invention; is to provide a process of. reactin naphthalene, benzene or phenols witholefines to produoe:alky lated naphthalenes; dialkyl benzenes; or alkylated phenols which areisomeri-c: products to obtain high. yields of'the desired isomers: without high losses ofraw. materials...

Another object of themventio-n is to provide a process of catalytically isomerizing a mixture of alkylated naphthalenes, or dialkylbenzenes, or alkylated phenols to obtain a high yield of the desired isomers without loss of raw material.

A further object of the invention is to provide a catalytic process of alkylating and/or isomerizing naphthalene with ethylene to obtain a high yield of betaethylnaphthalene with a low loss of raw materials.

Alpha and betaethylnaphthalenes form a eutectic mixture composed of 51% to 53% betaethylnaphthalene and 49 to 47% alphaethylnaphthalene. If an equilibrium mixture of 80% betaand 20% alphaethylnaphthalenes is crystallized in methyl alcohol pure betaethylnaphthalene will crystallize and separate so that it may be removed from the solution. The eutectic temperature is approximately 35 C. but the mixture dissolved in an equal weight of methyl alcohol may be cooled to 40 C. and still separate pure betaethylnaphthalene as a crystalline product while the eutectic mixture remains in the mother liquor. The betaethylnaphthalene crystals may be separated from the mother liquor and, thereafter the mother liquor may be isomerized with the improved silicaalumina-K2O catalyst toconvert the alphaethylnaphthalene to betaethylnaphthalene until an equilibrium mixture is again obtained.

Accordingly a further object of the invention is to provide a process of recovering pure betaethylnaphthalene from a mixture'of betaand alphaethylnaphthalene by crystallization and catalytic isomerization.

With these and other objects in view the invention consists in the improved process of isomerizing alkylated naphthalene, benzenes or phenols to obtain isomeric compounds and the separation of the isomers as herein described and particularly defined in the claims.

The present invention is more particularly adapted for the alkylation of aromatics, such as naphthalene, benzene and phenols to form alkylated naphthalenes, dialkylbenzenes and alkylated phenols which exist in two or more isomeric forms. The alkylation is preferably carried out by treating the aromatic compound with olefins which have 2 to 4 carbon atoms to the .molecule, such as ethylene, propylene, or butylene. The aromatic compound may be alkylated in the vapor phase or in the liquid phase by passing the mixture of aromatic compound with olefin with or without steam through a bed of solid catalyst composed of alumina-silica mixed with an alkaline compound of an alkali metal. The catalyst may be composed of to 12% A1202; 79 to 88% SiO2; and 2 to 9% K20.

The alumina-silica catalyst is composed oi" precipitated alumina and silica which is dried and then impregnated with potassium carbonate (K2CO3). As the catalyst is used in the isomerization reaction the alkali metal exists as K20, KOI-I, K2CO3, potassium aluminate and potassium silicate. When analyzing such a catalyst the product is reported as percentage of K20. In the claims the alkali metal is referred to as K2CO3 which includes K20, K2CO3, KOI-I, potassium aluminate and potassium silicate.

Both the alkylation and isomerization reactions may be carried out at temperatures of 275 to 650 C. At the lower temperature the formation of polyalkylated products is held at the minimum but the conversion is comparatively low. We have found that the alkylation and isomerization may be effectively carried out at 425 C. to obtain a good yield with a comparatively '4 small loss of material. Such a reaction may be carried out in the vapor phase at atmospheric pressure to produce substantially the equilibrium mixture.

The time of reaction may be much more effectively controlled by carrying on the reaction under pressure, that is a pressure of from 100 to 900 lbs. per square inch. The pressure, however, must be sufficient to keep the aromatic with the olefin dissolved therein in the liquid phase and preferably temperatures of 300 to 400 C. are used with pressures of 300 to 900 lbs. per square inch.

The accompanying drawing is a fiow sheet of the steps involved in the preferred form of the invention which embodies a combined alkylation and isomerization of naphthalene to produce a substantially pure betaethylnapthalene.

Referring to the drawing naphthalene in a container I0 is saturated with an olefine, such as ethylene, which is forced from a container E2 into the naphthalene. The solution of napthalene passes through a line I 4 from the container l0 into a catalyst bed 16 which is filled with a body of catalyst composed of a major por tion of silica, a minor portion of alumina, and a small portion of K20. The catalyst bed is maintained at a temperature of approximately 425 C. and if the combined alkylation and isomerization reaction is carried out in the vapor phase superheated steam in the ratio of one volume of napthalene-olefine vapors to ten volumes of steam passes through the catalyst bed It. In the catalyst bed a combined alkylation and isomerization reaction is carried out so that the vapor product fiows from the catalyst bed into an equilibrium mixture cooler I8. The equilibrium mixture is composed of substantially betaethylnaphthalene and 20% of alphaethylnaphthalene. Also in the mixture is collected any unreacted naphthalene.

,The equilibrium mixture flows from the cooler l8 through a line 20 into a crystallizer 22. An alcohol, such as methyl alcohol, from a container 24. is added to the equilibrium mixture to dissolve the mixture. In the crystallizer the temperature of the mixture is reduced to be tween -35 an 45 C. to crystallize betaethylnaphthalene and to leave in the crystallizer an eutectic mixture composed of substantially equal parts of alphaand beta-ethylnaphthalene. The eutectic mixture, however, may vary from 51 to 53% betaethylnaphthalene and 49% to 47% alphaethylnaphthalene. This eutectic mixture together with the unconverted naphthalene is decanted from the crystallizer and passes to a still 26 where the alcohol is removed overhead and passes to the container 24. The still bottoms comprise the eutectic mixture and these bottoms fiow from the still through a line 28 through a heater 3!! back to the line [4 where it is preferably vaporized to again pass into the catalytic conversion chamber IE to be isomerized. The betaethylnaphthalene crystallized in the crystallizer 22 is substantially pure betaethylnaphthalene and is withdrawn from the crystallizer through a line 32.

By the straight alkylation of naphthalene with ethylene as described above, an equilibrium mixture composed of 82% to 78% betaethylnaphthalene and 18 to 22% alphaethylnaphthalene is obtained. The eutectic mixture of the alphaand betae y phthalenes may be isomerized catalyticallywith the preferred catalyst as shown in the follow-i'ng table:

TABLE tive in alkyiating 'cresolsand xylenols, as well as the dialkylbenzenes.

omerz'zation of ethylnaphthalene with an alkalicontainin'g' alumina-silica catalyst-m 'vupo r phase using an ethylnaphthalene mixture composed of 5 alphaethylnaphthalene and 50% betaethylnaphthalene in which one vol ume-of' the ethylnaphth'alene vapor-mixture withten volumes o'f'st'e am are passe the catalyst conversion zonev d through Experimental Conditions:

CatalystUsed A]20(lSiO2 2.5% K2003 on Meow-Slog.

Catalyst Temp, C; 425 425 Length ofjR'un, Hrs; 36;

Product Distribution: Wt. Percent? Gases Carbon Composition of Liquid, Wt. Per- The catalyst used for the runs'shown'in the table above was composed. of 12.2% alumina and 87.8% silica forrun 1'. No metallic alkali was used forthis run. For run No. 2, 2.5% by weight of KzCOs, run No. 3, K2CO3 and run No. 4, 7.5% K2CO3'W616 added respectively to the same kind of alumina-silica catalyst used for run No. 1. These runs show a comparison of the yields and'products formed using different strengths of alkali. It will be seen that for run No. 1, 8.3% of polyethylnaphthalene was formed and 12.9% of the naphthalene was found in the reaction mixture. The ethylnaphthalene mixture contained 80.5% of betaethylnaphthalene. 1.5% of gases were formed and 2.2% of carbon was formed. In run No. 2 the ethylnaphthalene mixture contained 74.5 of betaethylnaphthalene. 5.7% of polyethylnaphthalenes was formed while 5.3% of naphthalene was found in the reaction mixture. The gases and carbon formed were comparatively low.

With 5% KzCOs in the catalyst the equilibrium mixture of alphaand betaethylnaphthalenes was formed, while the gas and carbon were very low and polyethylnaphthalene was only 1.7%. In run No. 4 the equilibrium mixture of betaethylnaphthalene was reached, the amounts of gas and carbon were very low, and substantially no naphthalene was found in the liquid product.

We have found that commercial yields of betaethylnaphthalene and alphaethylnaphthalene may be formed if of K2003 is added to the silica-alumina catalyst. However, the activity of the catalyst tends to fall quite rapidly when the K2003 is above 10% and experience shows that a weight of 2.5 to 7.5% of KzCOs is a very favorable amount of alkali to have present in the catalyst. The addition of 5 to 7.5% of KzCOa to the synthetic alumina-silica catalyst is equally effective for alkylation and isomerization, or a combination of both alkylation and isomerization.

The process of the present invention is described and illustrated specifically with reference to the alkylation of naphthalene to recover a pure betaethylnaphthalene. It has been found, however, that the present catalyst is very effec- When isomerizing alkylated phenols or hydrocarbons by the present process, it is necessary that the aromatic compound shall have two free valences by which the alkyl groups maybe transferred from one carbon atomto anothercarbon atom on the aromatic hydrocarbon ring. With the alkylated phenolstheOI-I- group is fixed and the isomerization reaction transfers the alkyl group from one carbon atom on the benzene ring to another carbon atomon the benzene ring not occupied by the OH- group. With naphthalene the first benzene ring is fixed while the isomerization transfers an alkyl group on the carbon atoms of the second benzene ring. With dialkylbenzene the alkyl groups are transferred into ortho-, meta-, and para-positions.

The preferred form of the invention having been thus described, what is claimed as new is:

1. A process of isomerizing aromatic compounds which exist in the form of two or more possible isomers having the formula in which R is an alkyl group and R is a group selected from the group consisting of alkyl, hydroxy, and a bivalent group forming a fused ring aromatic with two adjacent carbon atoms of the aromatic ring comprising: passing the aromatic compound with steam through a catalyst bed made up of a major portion of silica and a minor portion of alumina with from 3% to 10% by weight of the catalyst being an alkaline compound of an alkali metal.

2. The process defined in claim 1 in which the aromatic compound is isomerized in the vapor phase in the ratio of one volume of vapor of aromatic compound to 10 volumes of steam.

3. The process defined in claim 1 in which the alkali metal compound is K2003.

4. The process defined in claim 1 in which the alkali metal compound is 7.5% K2003 by weight of a synthetic catalyst composed of silica and alumina. I

5. The process defined in claim 1 in which the catalyst is composed by weight of 10 to 12% A1202, 79 to 88% S102 and 2.5 to 9% K20.

6. The process defined in claim 1 in which the reaction is carried out at a temperature between 300 and 600 C.

7. The process defined in claim 1 in which the reaction is carried out at a pressure of 300 to 900 lbs. per square inch and a temperature of 300 to 450 C. in liquid phase.

8. The process defined in claim 1 in which the aromatic compound is a eutectic mixture of alphaand betaethylnaphthalenes.

9. The process defined in claim 8 in which the reaction mixture is diluted with methanol, then cooled to a temperature below -35 C. to crystallize betaethylnaphthalene, separating the beta ethylnaphthalene, distilling the mother liquor to separate alcohol therefrom and adding the mother liquor to fresh chargin stock to be isomerized.

10. A process of alkylating and isomerizing aromatic compounds which exist in the form of two or more possible isomers having the formula in which R. is an alkyl group and R is a group selected from the groups consisting of alkyl, hydroxy, and a bivalent group forming a fused ring aromatic with two adjacent carbon atoms of the aromatic ring comprising: passing the aromaticcompound with an olefine having from two to four carbon atoms to the molecule and steam under suflicient pressure to maintain the compound in liquid phaseat a temperature of 300 to 600 C. through a catalyst bed made up of a major portion of S102 and a minor portion of A1203 with from 3% to 10% by weight of K20 based on the weight of the alumina and silica, diluting the reaction mixture with an aliphatic alcohol, freezing the mixture to crystallize one of the isomers formed by alkylation, separating the crystals, evaporating alcohol from the mother liquor and isomerizing the mother liquor by passing it at a temperature of 300 to 600 C. through a bed of said alkylation catalyst.

11. The process defined in claim 10 in which the compound is naphthalene and the olefin is ethylene.

12. A process for isomerizing ethylnaphthalene comprising: passing the ethylnaphthalene with steam through a catalyst bed made up of a major portion of silica and a minor portion of alumina with from 3 to 10 per cent by weight of the catalyst being an alkaline compound of an alkali metal.

BEN BENNETT CORSON. JOSEPH E. NTCKELS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Swietoslawski Sept. 30, 1947 

1. A PROCESS OF ISOMERIZING AROMATIC COMPOUNDS WHICH EXIST IN THE FORM OF TWO OR MORE POSSIBLE ISOMERS HAVING THE FORMULA 